1. Field of the Invention
The present invention relates to the technology field of inverter systems, and more particularly to an inverter system for energy-storing microgrid and controlling method thereof.
2. Description of the Prior Art
Inverter is used for converting DC energy to a high-quality AC power. For establishing an inverter system having high capability and capable of providing high-quality AC power, it carries out the establishment by parallel connecting multi inverters having small capability. However, because the unequal distribution of the inverter currents always occur in the high-capability inverter system established by parallel connecting multi inverters, how to solve the problem of the unequal distribution of the inverter currents has been became the most important issue.
Currently, the controlling methods for parallel inverter system are mainly divided into active current distribution method and voltage-reducing method. When using the active current distribution method to control the parallel inverter system, each inverter current of the parallel inverters would track a reference current, such that each of the parallel inverters are equivalent to a current source, so as to steady the output currents of the parallel inverter system. However, since the parallel inverters in the parallel inverter system are coupled to the reference current source via transmission lines, the transmitted reference currents in the transmission lines would subject to noise interference resulted from over-long transmission lines, and that would impact the stability and reliability of the parallel inverter system.
Inheriting to above descriptions, both the problems of noise interference and signal delay produced by the over-long transmission lines can be solved by way of noise filter and signal process; however, it would cause the inverter system unable to work normally when the transmission lines failure or break down, and that may be the primary concern as the inverter system is applied. On the other hand, the primary drawback of the voltage-reducing method is that the capacitance state of the input-end battery modules of the inverter system does not be considered when the method is used to distribute the current supply of each of the battery modules, and that would reduce lifetime of certain battery modules and eventually result in the breakdown of the battery modules.
Accordingly, in view of the conventional active current distribution method and voltage-reducing method still including drawbacks and shortcomings, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided an inverter system for energy-storing microgrid and controlling method thereof.